Insert Molding of Bulk Amorphous Alloy into Open Cell Foam

ABSTRACT

Provided in one embodiment is a method of making use of foams as a processing aid or to improve the properties of bulk-solidifying amorphous alloy materials. Other embodiments include the bulk-solidifying amorphous alloy/foam composite materials made in accordance with the methods.

FIELD OF INVENTION

This invention relates to methods of making use of open cell foams as aprocessing aid or to improve the properties of bulk-solidifyingamorphous alloy materials, and to the materials made therefrom.

BACKGROUND

Bulk-solidifying amorphous alloys have been made in a variety of metalsystems. They are generally prepared by quenching from above the meltingtemperature to the ambient temperature. Generally, high cooling rates onthe order of 10⁵° C./sec, are needed to achieve an amorphous structure.The lowest rate by which a bulk solidifying alloy can be cooled to avoidcrystallization, thereby achieving and maintaining the amorphousstructure during cooling, is referred to as the “critical cooling rate”for the alloy. In order to achieve a cooling rate higher than thecritical cooling rate, heat has to be extracted from the sample. Thus,the thickness of articles made from amorphous alloys often becomes alimiting dimension, which is generally referred to as the “critical(casting) thickness.” A critical casting thickness can be obtained byheat-flow calculations, taking into account the critical cooling rate.

Until the early nineties, the processability of amorphous alloys wasquite limited, and amorphous alloys were readily available only inpowder form or in very thin foils or strips with a critical castingthickness of less than 100 micrometers. A new class of amorphous alloysbased mostly on Zr and Ti alloy systems was developed in the nineties,and since then more amorphous alloy systems based on different elementshave been developed. These families of alloys have much lower criticalcooling rates of less than 10³° C./sec, and thus these articles havemuch larger critical casting thicknesses than their previouscounterparts. The bulk-solidifying amorphous alloys are capable of beingshaped into a variety of forms, thereby providing a unique advantage inpreparing intricately designed parts.

One feature of the bulk-solidifying amorphous alloy that has somewhatlimited its use is that it has a relatively small critical castingthickness. That is, the overall thickness of bulk-solidifying amorphousmaterial that can be cast is relatively small, thus limiting its use forthicker casting parts. In addition, bulk-solidifying amorphous material,while extremely hard and capable of being more elastically deformed thanother hard metals, also are brittle. Accordingly, thin layers ofbulk-solidifying amorphous alloy materials may be susceptible to cracksor other deformities when subjected to stress.

Foams and other highly porous materials with a cellular structure areknown to have many interesting combinations of physical and mechanicalproperties, such as high stiffness in conjunction with very low specificweight or high gas permeability combined with high thermal conductivity.Among man-made cellular materials, polymeric foams are currently themost important ones with widespread applications in nearly every sectorof technology. Metals and alloys may also be produced as cellularmaterials or foams.

There are many ways to manufacture cellular metallic materials. Somemethods are similar to techniques used for foaming aqueous or polymerliquids, whereas others are specially designed by taking advantage ofcharacteristic properties of metals such as their sintering activity orthe fact that they can be electrically deposited. The various methodscan be classified according to the state in which the metal isprocessed. The four “families” of processes are as follows: (i) fromliquid metal, (ii) from solid metal in powdered form, (iii) from metalvapor or gaseous metallic compounds, and (iv) from a metal ion solution.

Powder metallurgy is a method of forming conventional closed cell foamswhere the starting materials are metal powders and where the actualfoaming takes place in the liquid state. The production process beginswith the mixing of metal powders, which can be made up of elementarymetal powders, alloy powders or metal powder blends in the presence of ablowing or foaming agent. Afterwards the mix is compacted to yield adense, semi-finished product. In principle, the compaction can be doneby any technique that ensures that the blowing agent is embedded intothe metal matrix without any notable residual open porosity. Examples ofsuch compaction methods are hot uniaxial or isostatic compression, rodextrusion or powder rolling. Which compaction method is chosen dependson the required shape of the precursor material. Rectangular profileswith various cross-sections may be made, from which thin sheets can thenbe formed by rolling. The manufacture of the precursor has to be carriedout carefully because any residual porosity or other defects may lead topoor results in further processing.

Heat treatment at temperatures near the melting point of the matrixmaterial is the next step in the powder metallurgy process. The blowingor foaming agent, which is homogeneously distributed within the densemetallic matrix, decomposes at these temperatures. The released gasforces the compacted precursor material to expand, thus forming itshighly porous structure.

The method is not restricted to aluminum and its alloys. Tin, zinc,brass, lead, gold and some other metals and alloys can also be foamed bychoosing appropriate blowing agents and process parameters. The mostcommon alloys for foaming are pure aluminum or wrought alloys. Castingalloys such as AlSi₇Mg (A356) and AlSi₁₂ are also frequently usedbecause of their low melting point and good foaming properties.

U.S. Pat. No. 5,302,414 to Alkhimov et al., herein incorporated byreference in its entirety, discloses a cold gas-dynamic spraying methodfor applying a coating to an article by introducing into a gas,particles of a powder of a metal, alloy, polymer or mechanical mixtureof a metal and an alloy. The gas and particles are formed into asupersonic jet having a temperature considerably below a fusingtemperature of the powder material and a velocity of from about 300 toabout 1,200 m/sec. The jet is then directed against an article of ametal, alloy or dielectric, thereby coating the article with theparticles.

U.S. Pat. No. 6,408,928 to Heinrich et al., herein incorporated byreference in its entirety, discloses an apparatus for producingexpandable metal, comprising (1) means for feeding a powder mixturecontaining at least one metal powder and at least one blowing agent inpowder form; (2) means for producing a compact body from the powdermixture; and (3) means for heating the compact body to a temperatureequal to or above the breakdown temperature of the blowing agent. Thecold-gas spray apparatus can be used to form metal foams obtained fromthe foamable metal bodies.

U.S. Pat. No. 6,464,933 to Popoola et al., herein incorporated byreference in its entirety, discloses a method of fabricating a foamedmetal structure using a supply of metal particles. The method comprisesthe steps of (a) introducing a supply of powder metal particles andfoaming agent particles into a propellant gas to form a gas/particlemixture; (b) projecting the mixture at or above a critical velocity ofat least sonic velocity onto a metallic substrate to create a deposit ofpressure-compacted metal particles containing the admixed foaming agent;and (c) subjecting at least the coating on said substrate to a thermalexcursion effective to activate expansion of the foaming agent whilesoftening the metal particles for plastic deformation under theinfluence of the expanding gases.

A process for manufacturing a foamed article is described in WO 01/62416A1, according to which an ingot mold is filled with foam by collectingindividual bubbles rising in the melt. However, this process, in whichthe gas bubbles are introduced and isolated for the most part by way ofa so-called rotor impeller, has the disadvantages that, on the one hand,filling the ingot mold is slow and, therefore, with a cooled ingot moldwall, the part of the article that was formed last has a frequentlydisadvantageously thick wall layer, and, on the other hand, the bubblesize is embodied variably in an uncontrolled manner. As a result, themechanical characteristic values of a part or article created in thismanner often feature a great dispersion that is unfavorable for the mostpart.

It would be desirable to provide a method for processingbulk-solidifying amorphous alloy materials together with metal foams toprovide new materials having improved properties and processability.

SUMMARY

A proposed solution according to embodiments herein is to provide amethod of forming an article that includes a foam having insert moldedthereon and/or therein a bulk-solidifying amorphous alloy. In accordancewith one embodiment, there is provided a method of making an articlethat includes providing a foam material, and insert casting onto thefoam material a bulk-solidifying amorphous alloy to form the article.

In accordance with another embodiment, there is provided a method ofmaking an article that includes providing a foam material, insertcasting onto the foam material a bulk-solidifying amorphous alloy,removing the foam, and optionally inserting another metal orbulk-solidifying amorphous alloy to replace the removed foam.

In accordance with another embodiment, there is provided an articlecomprised of a bulk-solidifying amorphous alloy and a foam. In oneembodiment, the article includes of a laminate of bulk-solidifyingamorphous alloy and a foam. In another embodiment, the article includesa bulk-solidifying amorphous alloy having a thickness greater than thecritical casting thickness, optionally including a foam, or havingdispersed therein a metal or a bulk-solidifying amorphous alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a temperature-viscosity diagram of an exemplary bulksolidifying amorphous alloy.

FIG. 2 provides a schematic of a time-temperature-transformation (TTT)diagram for an exemplary bulk solidifying amorphous alloy.

FIG. 3 is an electron scanning micrograph of an open cell metal foam.

FIG. 4 provides a schematic of a method of making an article inaccordance with an embodiment.

FIG. 5 is perspective view of an illustrative portable electronic devicehaving a housing made with an article in accordance with an embodiment.

DETAILED DESCRIPTION

All publications, patents, and patent applications cited in thisSpecification are hereby incorporated by reference in their entirety.

The articles “a” and “an” are used herein to refer to one or to morethan one (i.e., to at least one) of the grammatical object of thearticle. By way of example, “a polymer resin” means one polymer resin ormore than one polymer resin. Any ranges cited herein are inclusive. Theterms “substantially” and “about” used throughout this Specification areused to describe and account for small fluctuations. For example, theycan refer to less than or equal to ±5%, such as less than or equal to±2%, such as less than or equal to ±1%, such as less than or equal to±0.5%, such as less than or equal to ±0.2%, such as less than or equalto ±0.1%, such as less than or equal to ±0.05%.

Bulk-solidifying amorphous alloys, or bulk metallic glasses (“BMG”), area recently developed class of metallic materials. These alloys may besolidified and cooled at relatively slow rates, and they retain theamorphous, non-crystalline (i.e., glassy) state at room temperature.Amorphous alloys have many superior properties than their crystallinecounterparts. However, if the cooling rate is not sufficiently high,crystals may form inside the alloy during cooling, so that the benefitsof the amorphous state can be lost. For example, one challenge with thefabrication of bulk amorphous alloy parts is partial crystallization ofthe parts due to either slow cooling or impurities in the raw alloymaterial. As a high degree of amorphicity (and, conversely, a low degreeof crystallinity) is desirable in BMG parts, there is a need to developmethods for casting BMG parts having controlled amount of amorphicity.

FIG. 1 (obtained from U.S. Pat. No. 7,575,040) shows aviscosity-temperature graph of an exemplary bulk solidifying amorphousalloy, from the VIT-001 series of Zr—Ti—Ni—Cu—Be family manufactured byLiquidmetal Technology. It should be noted that there is no clearliquid/solid transformation for a bulk solidifying amorphous metalduring the formation of an amorphous solid. The molten alloy becomesmore and more viscous with increasing undercooling until it approachessolid form around the glass transition temperature. Accordingly, thetemperature of solidification front for bulk solidifying amorphousalloys can be around glass transition temperature, where the alloy willpractically act as a solid for the purposes of pulling out the quenchedamorphous sheet product.

FIG. 2 (obtained from U.S. Pat. No. 7,575,040) shows thetime-temperature-transformation (TTT) cooling curve of an exemplary bulksolidifying amorphous alloy, or TTT diagram. Bulk-solidifying amorphousmetals do not experience a liquid/solid crystallization transformationupon cooling, as with conventional metals. Instead, the highly fluid,non crystalline form of the metal found at high temperatures (near a“melting temperature” Tm) becomes more viscous as the temperature isreduced (near to the glass transition temperature Tg), eventually takingon the outward physical properties of a conventional solid.

Even though there is no liquid/crystallization transformation for a bulksolidifying amorphous metal, a “melting temperature” Tm may be definedas the thermodynamic liquidus temperature of the correspondingcrystalline phase. Under this regime, the viscosity of bulk-solidifyingamorphous alloys at the melting temperature could lie in the range ofabout 0.1 poise to about 10,000 poise, and even sometimes under 0.01poise. A lower viscosity at the “melting temperature” would providefaster and complete filling of intricate portions of the shell/mold witha bulk solidifying amorphous metal for forming the BMG parts.Furthermore, the cooling rate of the molten metal to form a BMG part hasto such that the time-temperature profile during cooling does nottraverse through the nose-shaped region bounding the crystallized regionin the TTT diagram of FIG. 2. In FIG. 2, Those is the criticalcrystallization temperature Tx where crystallization is most rapid andoccurs in the shortest time scale.

The supercooled liquid region, the temperature region between Tg and Txis a manifestation of the extraordinary stability againstcrystallization of bulk solidification alloys. In this temperatureregion the bulk solidifying alloy can exist as a high viscous liquid.The viscosity of the bulk solidifying alloy in the supercooled liquidregion can vary between 10¹² Pa s at the glass transition temperaturedown to 10⁵ Pa s at the crystallization temperature, the hightemperature limit of the supercooled liquid region. Liquids with suchviscosities can undergo substantial plastic strain under an appliedpressure. The embodiments herein make use of the large plasticformability in the supercooled liquid region as a forming and separatingmethod.

One needs to clarify something about Tx. Technically, the nose-shapedcurve shown in the TTT diagram describes Tx as a function of temperatureand time. Thus, regardless of the trajectory that one takes whileheating or cooling a metal alloy, when one hits the TTT curve, one hasreached Tx. In FIG. 2, Tx is shown as a dashed line as Tx can vary fromclose to Tm to close to Tg.

The schematic TTT diagram of FIG. 2 shows processing methods of diecasting from at or above Tm to below Tg without the time-temperaturetrajectory (shown as (1) as an example trajectory) hitting the TTTcurve. During die casting, the forming takes place substeantiallysimultaneously with fast cooling to avoid the trajectory hitting the TTTcurve. The procssing methods for superplastic forming (SPF) from at orbelow Tg to below Tm without the time-temperature trajectory (shown as(2), (3) and (4) as example trajectories) hitting the TTT curve. In SPF,the amorphous BMG is reheated into the supercooled liquid region wherethe available processing window could be much larger than die casting,resulting in better controllability of the process. The SPF process doesnot require fast cooling to avoid crystallization during cooling. Also,as shown by example trajectories (2), (3) and (4), the SPF can becarried out with the highest temperature during SPF being above Tnose orbelow Tnose, up to about Tm. If one heats up a piece of amorphous alloybut manages to avoid hitting the TTT curve, you have heated “between Tgand Tm”, but one would have not reached Tx.

Typical differential scanning calorimeter (DSC) heating curves ofbulk-solidifying amorphous alloys taken at a heating rate of 20 C/mindescribe, for the most part, a particular trajectory across the TTT datawhere one would likely see a Tg at a certain temperature, a Tx when theDSC heating ramp crosses the TTT crystallization onset, and eventuallymelting peaks when the same trajectory crosses the temperature range formelting. If one heats a bulk-solidifying amorphous alloy at a rapidheating rate as shown by the ramp up portion of trajectories (2), (3)and (4) in FIG. 2, then one could avoid the TTT curve entirely, and theDSC data would show a glass transition but no Tx upon heating. Anotherway to think about it is trajectories (2), (3) and (4) can fall anywherein temperature between the nose of the TTT curve (and even above it) andthe Tg line, as long as it does not hit the crystallization curve. Thatjust means that the horizontal plateau in trajectories might get muchshorter as one increases the processing temperature.

Phase

The term “phase” herein can refer to one that can be found in athermodynamic phase diagram. A phase is a region of space (e.g., athermodynamic system) throughout which all physical properties of amaterial are essentially uniform. Examples of physical propertiesinclude density, index of refraction, chemical composition and latticeperiodicity. A simple description of a phase is a region of materialthat is chemically uniform, physically distinct, and/or mechanicallyseparable. For example, in a system consisting of ice and water in aglass jar, the ice cubes are one phase, the water is a second phase, andthe humid air over the water is a third phase. The glass of the jar isanother separate phase. A phase can refer to a solid solution, which canbe a binary, tertiary, quaternary, or more, solution, or a compound,such as an intermetallic compound. As another example, an amorphousphase is distinct from a crystalline phase.

Metal, Transition Metal, and Non-Metal

The term “metal” refers to an electropositive chemical element. The term“element” in this Specification refers generally to an element that canbe found in a Periodic Table. Physically, a metal atom in the groundstate contains a partially filled band with an empty state close to anoccupied state. The term “transition metal” is any of the metallicelements within Groups 3 to 12 in the Periodic Table that have anincomplete inner electron shell and that serve as transitional linksbetween the most and the least electropositive in a series of elements.Transition metals are characterized by multiple valences, coloredcompounds, and the ability to form stable complex ions. The term“nonmetal” refers to a chemical element that does not have the capacityto lose electrons and form a positive ion.

Depending on the application, any suitable nonmetal elements, or theircombinations, can be used. The alloy (or “alloy composition”) cancomprise multiple nonmetal elements, such as at least two, at leastthree, at least four, or more, nonmetal elements. A nonmetal element canbe any element that is found in Groups 13-17 in the Periodic Table. Forexample, a nonmetal element can be any one of F, Cl, Br, I, At, O, S,Se, Te, Po, N, P, As, Sb, Bi, C, Si, Ge, Sn, Pb, and B. Occasionally, anonmetal element can also refer to certain metalloids (e.g., B, Si, Ge,As, Sb, Te, and Po) in Groups 13-17. In one embodiment, the nonmetalelements can include B, Si, C, P, or combinations thereof. Accordingly,for example, the alloy can comprise a boride, a carbide, or both.

A transition metal element can be any of scandium, titanium, vanadium,chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium,zirconium, niobium, molybdenum, technetium, ruthenium, rhodium,palladium, silver, cadmium, hafnium, tantalum, tungsten, rhenium,osmium, iridium, platinum, gold, mercury, rutherfordium, dubnium,seaborgium, bohrium, hassium, meitnerium, ununnilium, unununium, andununbium. In one embodiment, a BMG containing a transition metal elementcan have at least one of Sc, Y, La, Ac, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd,and Hg. Depending on the application, any suitable transitional metalelements, or their combinations, can be used. The alloy composition cancomprise multiple transitional metal elements, such as at least two, atleast three, at least four, or more, transitional metal elements.

The presently described alloy or alloy “sample” or “specimen” alloy canhave any shape or size. For example, the alloy can have a shape of aparticulate, which can have a shape such as spherical, ellipsoid,wire-like, rod-like, sheet-like, flake-like, or an irregular shape. Theparticulate can have any size. For example, it can have an averagediameter of between about 1 micron and about 100 microns, such asbetween about 5 microns and about 80 microns, such as between about 10microns and about 60 microns, such as between about 15 microns and about50 microns, such as between about 15 microns and about 45 microns, suchas between about 20 microns and about 40 microns, such as between about25 microns and about 35 microns. For example, in one embodiment, theaverage diameter of the particulate is between about 25 microns andabout 44 microns. In some embodiments, smaller particulates, such asthose in the nanometer range, or larger particulates, such as thosebigger than 100 microns, can be used.

The alloy sample or specimen can also be of a much larger dimension. Forexample, it can be a bulk structural component, such as an ingot,housing/casing of an electronic device or even a portion of a structuralcomponent that has dimensions in the millimeter, centimeter, or meterrange.

Solid Solution

The term “solid solution” refers to a solid form of a solution. The term“solution” refers to a mixture of two or more substances, which may besolids, liquids, gases, or a combination of these. The mixture can behomogeneous or heterogeneous. The term “mixture” is a composition of twoor more substances that are combined with each other and are generallycapable of being separated. Generally, the two or more substances arenot chemically combined with each other.

Alloy

In some embodiments, the alloy composition described herein can be fullyalloyed. In one embodiment, an “alloy” refers to a homogeneous mixtureor solid solution of two or more metals, the atoms of one replacing oroccupying interstitial positions between the atoms of the other; forexample, brass is an alloy of zinc and copper. An alloy, in contrast toa composite, can refer to a partial or complete solid solution of one ormore elements in a metal matrix, such as one or more compounds in ametallic matrix. The term alloy herein can refer to both a completesolid solution alloy that can give single solid phase microstructure anda partial solution that can give two or more phases. An alloycomposition described herein can refer to one comprising an alloy or onecomprising an alloy-containing composite.

Thus, a fully alloyed alloy can have a homogenous distribution of theconstituents, be it a solid solution phase, a compound phase, or both.The term “fully alloyed” used herein can account for minor variationswithin the error tolerance. For example, it can refer to at least 90%alloyed, such as at least 95% alloyed, such as at least 99% alloyed,such as at least 99.5% alloyed, such as at least 99.9% alloyed. Thepercentage herein can refer to either volume percent or weightpercentage, depending on the context. These percentages can be balancedby impurities, which can be in terms of composition or phases that arenot a part of the alloy.

Amorphous or Non-Crystalline Solid

An “amorphous” or “non-crystalline solid” is a solid that lacks latticeperiodicity, which is characteristic of a crystal. As used herein, an“amorphous solid” includes “glass” which is an amorphous solid thatsoftens and transforms into a liquid-like state upon heating through theglass transition. Generally, amorphous materials lack the long-rangeorder characteristic of a crystal, though they can possess someshort-range order at the atomic length scale due to the nature ofchemical bonding. The distinction between amorphous solids andcrystalline solids can be made based on lattice periodicity asdetermined by structural characterization techniques such as x-raydiffraction and transmission electron microscopy.

The terms “order” and “disorder” designate the presence or absence ofsome symmetry or correlation in a many-particle system. The terms“long-range order” and “short-range order” distinguish order inmaterials based on length scales.

The strictest form of order in a solid is lattice periodicity: a certainpattern (the arrangement of atoms in a unit cell) is repeated again andagain to form a translationally invariant tiling of space. This is thedefining property of a crystal. Possible symmetries have been classifiedin 14 Bravais lattices and 230 space groups.

Lattice periodicity implies long-range order. If only one unit cell isknown, then by virtue of the translational symmetry it is possible toaccurately predict all atomic positions at arbitrary distances. Theconverse is generally true, except, for example, in quasi-crystals thathave perfectly deterministic tilings but do not possess latticeperiodicity.

Long-range order characterizes physical systems in which remote portionsof the same sample exhibit correlated behavior. This can be expressed asa correlation function, namely the spin-spin correlation function: G(x,x′)=

s(x), s(x′)

.

In the above function, s is the spin quantum number and x is thedistance function within the particular system. This function is equalto unity when x=x′ and decreases as the distance |x−x′| increases.Typically, it decays exponentially to zero at large distances, and thesystem is considered to be disordered. If, however, the correlationfunction decays to a constant value at large |x−x′|, then the system canbe said to possess long-range order. If it decays to zero as a power ofthe distance, then it can be called quasi-long-range order. Note thatwhat constitutes a large value of |x−x′| is relative.

A system can be said to present quenched disorder when some parametersdefining its behavior are random variables that do not evolve with time(i.e., they are quenched or frozen)—e.g., spin glasses. It is oppositeto annealed disorder, where the random variables are allowed to evolvethemselves. Embodiments herein include systems comprising quencheddisorder.

The alloy described herein can be crystalline, partially crystalline,amorphous, or substantially amorphous. For example, the alloysample/specimen can include at least some crystallinity, withgrains/crystals having sizes in the nanometer and/or micrometer ranges.Alternatively, the alloy can be substantially amorphous, such as fullyamorphous. In one embodiment, the alloy composition is at leastsubstantially not amorphous, such as being substantially crystalline,such as being entirely crystalline.

In one embodiment, the presence of a crystal or a plurality of crystalsin an otherwise amorphous alloy can be construed as a “crystallinephase” therein. The degree of crystallinity (or “crystallinity” forshort in some embodiments) of an alloy can refer to the amount of thecrystalline phase present in the alloy. The degree can refer to, forexample, a fraction of crystals present in the alloy. The fraction canrefer to volume fraction or weight fraction, depending on the context. Ameasure of how “amorphous” an amorphous alloy is can be amorphicity.Amorphicity can be measured in terms of a degree of crystallinity. Forexample, in one embodiment, an alloy having a low degree ofcrystallinity can be said to have a high degree of amorphicity. In oneembodiment, for example, an alloy having 60 vol % crystalline phase canhave a 40 vol % amorphous phase.

Amorphous Alloy or Amorphous Metal

An “amorphous alloy” is an alloy having an amorphous content of morethan 50% by volume, preferably more than 90% by volume of amorphouscontent, more preferably more than 95% by volume of amorphous content,and most preferably more than 99% to almost 100% by volume of amorphouscontent. Note that, as described above, an alloy high in amorphicity isequivalently low in degree of crystallinity. An “amorphous metal” is anamorphous metal material with a disordered atomic-scale structure. Incontrast to most metals, which are crystalline and therefore have ahighly ordered arrangement of atoms, amorphous alloys arenon-crystalline. Materials in which such a disordered structure isproduced directly from the liquid state during cooling are sometimesreferred to as “glasses.” Accordingly, amorphous metals are commonlyreferred to as “metallic glasses” or “glassy metals.” In one embodiment,a bulk metallic glass (“BMG”) can refer to an alloy, of which themicrostructure is at least partially amorphous. However, there areseveral ways besides extremely rapid cooling to produce amorphousmetals, including physical vapor deposition, solid-state reaction, ionirradiation, melt spinning, and mechanical alloying. Amorphous alloyscan be a single class of materials, regardless of how they are prepared.

Amorphous metals can be produced through a variety of quick-coolingmethods. For instance, amorphous metals can be produced by sputteringmolten metal onto a spinning metal disk. The rapid cooling, on the orderof millions of degrees a second, can be too fast for crystals to form,and the material is thus “locked in” a glassy state. Also, amorphousmetals/alloys can be produced with critical cooling rates low enough toallow formation of amorphous structures in thick layers—e.g., bulkmetallic glasses.

The terms “bulk metallic glass” (“BMG”), bulk amorphous alloy (“BAA”),and bulk solidifying amorphous alloy are used interchangeably herein.They refer to amorphous alloys having the smallest dimension at least inthe millimeter range. For example, the dimension can be at least about0.5 mm, such as at least about 1 mm, such as at least about 2 mm, suchas at least about 4 mm, such as at least about 5 mm, such as at leastabout 6 mm, such as at least about 8 mm, such as at least about 10 mm,such as at least about 12 mm. Depending on the geometry, the dimensioncan refer to the diameter, radius, thickness, width, length, etc. A BMGcan also be a metallic glass having at least one dimension in thecentimeter range, such as at least about 1.0 cm, such as at least about2.0 cm, such as at least about 5.0 cm, such as at least about 10.0 cm.In some embodiments, a BMG can have at least one dimension at least inthe meter range. A BMG can take any of the shapes or forms describedabove, as related to a metallic glass. Accordingly, a BMG describedherein in some embodiments can be different from a thin film made by aconventional deposition technique in one important aspect—the former canbe of a much larger dimension than the latter.

Amorphous metals can be an alloy rather than a pure metal. The alloysmay contain atoms of significantly different sizes, leading to low freevolume (and therefore having viscosity up to orders of magnitude higherthan other metals and alloys) in a molten state. The viscosity preventsthe atoms from moving enough to form an ordered lattice. The materialstructure may result in low shrinkage during cooling and resistance toplastic deformation. The absence of grain boundaries, the weak spots ofcrystalline materials in some cases, may, for example, lead to betterresistance to wear and corrosion. In one embodiment, amorphous metals,while technically glasses, may also be much tougher and less brittlethan oxide glasses and ceramics.

Thermal conductivity of amorphous materials may be lower than that oftheir crystalline counterparts. To achieve formation of an amorphousstructure even during slower cooling, the alloy may be made of three ormore components, leading to complex crystal units with higher potentialenergy and lower probability of formation. The formation of amorphousalloy can depend on several factors: the composition of the componentsof the alloy; the atomic radius of the components (preferably with asignificant difference of over 12% to achieve high packing density andlow free volume); and the negative heat of mixing the combination ofcomponents, inhibiting crystal nucleation and prolonging the time themolten metal stays in a supercooled state. However, as the formation ofan amorphous alloy is based on many different variables, it can bedifficult to make a prior determination of whether an alloy compositionwould form an amorphous alloy.

Amorphous alloys, for example, of boron, silicon, phosphorus, and otherglass formers with magnetic metals (iron, cobalt, nickel) may bemagnetic, with low coercivity and high electrical resistance. The highresistance leads to low losses by eddy currents when subjected toalternating magnetic fields, a property useful, for example, astransformer magnetic cores.

Amorphous alloys may have a variety of potentially useful properties. Inparticular, they tend to be stronger than crystalline alloys of similarchemical composition, and they can sustain larger reversible (“elastic”)deformations than crystalline alloys. Amorphous metals derive theirstrength directly from their non-crystalline structure, which can havenone of the defects (such as dislocations) that limit the strength ofcrystalline alloys. For example, one modern amorphous metal, known asVitreloy™, has a tensile strength that is almost twice that ofhigh-grade titanium. In some embodiments, metallic glasses at roomtemperature are not ductile and tend to fail suddenly when loaded intension, which limits the material applicability in reliability-criticalapplications, as the impending failure is not evident. Therefore, toovercome this challenge, metal matrix composite materials having ametallic glass matrix containing dendritic particles or fibers of aductile crystalline metal can be used. Alternatively, a BMG low inelement(s) that tend to cause embitterment (e.g., Ni) can be used. Forexample, a Ni-free BMG can be used to improve the ductility of the BMG.

Another useful property of bulk amorphous alloys is that they can betrue glasses; in other words, they can soften and flow upon heating.This can allow for easy processing, such as by injection molding, inmuch the same way as polymers. As a result, amorphous alloys can be usedfor making sports equipment, medical devices, electronic components andequipment, and thin films. Thin films of amorphous metals can bedeposited as protective coatings via a high velocity oxygen fueltechnique.

A material can have an amorphous phase, a crystalline phase, or both.The amorphous and crystalline phases can have the same chemicalcomposition and differ only in the microstructure—i.e., one amorphousand the other crystalline. Microstructure in one embodiment refers tothe structure of a material as revealed by a microscope at 25×magnification or higher. Alternatively, the two phases can havedifferent chemical compositions and microstructures. For example, acomposition can be partially amorphous, substantially amorphous, orcompletely amorphous.

As described above, the degree of amorphicity (and conversely the degreeof crystallinity) can be measured by fraction of crystals present in thealloy. The degree can refer to volume fraction of weight fraction of thecrystalline phase present in the alloy. A partially amorphouscomposition can refer to a composition of at least about 5 vol % ofwhich is of an amorphous phase, such as at least about 10 vol %, such asat least about 20 vol %, such as at least about 40 vol %, such as atleast about 60 vol %, such as at least about 80 vol %, such as at leastabout 90 vol %. The terms “substantially” and “about” have been definedelsewhere in this application. Accordingly, a composition that is atleast substantially amorphous can refer to one of which at least about90 vol % is amorphous, such as at least about 95 vol %, such as at leastabout 98 vol %, such as at least about 99 vol %, such as at least about99.5 vol %, such as at least about 99.8 vol %, such as at least about99.9 vol %. In one embodiment, a substantially amorphous composition canhave some incidental, insignificant amount of crystalline phase presenttherein.

In one embodiment, an amorphous alloy composition can be homogeneouswith respect to the amorphous phase. A substance that is uniform incomposition is homogeneous. This is in contrast to a substance that isheterogeneous. The term “composition” refers to the chemical compositionand/or microstructure in the substance. A substance is homogeneous whena volume of the substance is divided in half and both halves havesubstantially the same composition. For example, a particulatesuspension is homogeneous when a volume of the particulate suspension isdivided in half and both halves have substantially the same volume ofparticles. However, it might be possible to see the individual particlesunder a microscope. Another example of a homogeneous substance is airwhere different ingredients therein are equally suspended, though theparticles, gases and liquids in air can be analyzed separately orseparated from air.

A composition that is homogeneous with respect to an amorphous alloy canrefer to one having an amorphous phase substantially uniformlydistributed throughout its microstructure. In other words, thecomposition macroscopically comprises a substantially uniformlydistributed amorphous alloy throughout the composition. In analternative embodiment, the composition can be of a composite, having anamorphous phase having therein a non-amorphous phase. The non-amorphousphase can be a crystal or a plurality of crystals. The crystals can bein the form of particulates of any shape, such as spherical, ellipsoid,wire-like, rod-like, sheet-like, flake-like, or an irregular shape. Inone embodiment, it can have a dendritic form. For example, an at leastpartially amorphous composite composition can have a crystalline phasein the shape of dendrites dispersed in an amorphous phase matrix; thedispersion can be uniform or non-uniform, and the amorphous phase andthe crystalline phase can have the same or a different chemicalcomposition. In one embodiment, they have substantially the samechemical composition. In another embodiment, the crystalline phase canbe more ductile than the BMG phase.

The methods described herein can be applicable to any type of amorphousalloy. Similarly, the amorphous alloy described herein as a constituentof a composition or article can be of any type. The amorphous alloy cancomprise the element Zr, Hf, Ti, Cu, Ni, Pt, Pd, Fe, Mg, Au, La, Ag, Al,Mo, Nb, Be, or combinations thereof. Namely, the alloy can include anycombination of these elements in its chemical formula or chemicalcomposition. The elements can be present at different weight or volumepercentages. For example, an iron “based” alloy can refer to an alloyhaving a non-insignificant weight percentage of iron present therein,the weight percent can be, for example, at least about 20 wt %, such asat least about 40 wt %, such as at least about 50 wt %, such as at leastabout 60 wt %, such as at least about 80 wt %. Alternatively, in oneembodiment, the above-described percentages can be volume percentages,instead of weight percentages. Accordingly, an amorphous alloy can bezirconium-based, titanium-based, platinum-based, palladium-based,gold-based, silver-based, copper-based, iron-based, nickel-based,aluminum-based, molybdenum-based, and the like. The alloy can also befree of any of the aforementioned elements to suit a particular purpose.For example, in some embodiments, the alloy, or the compositionincluding the alloy, can be substantially free of nickel, aluminum,titanium, beryllium, or combinations thereof. In one embodiment, thealloy or the composite is completely free of nickel, aluminum, titanium,beryllium, or combinations thereof.

For example, the amorphous alloy can have the formula (Zr, Ti)_(a)(Ni,Cu, Fe)_(b)(Be, Al, Si, B)_(c), wherein a, b, and c each represents aweight or atomic percentage. In one embodiment, a is in the range offrom 30 to 75, b is in the range of from 5 to 60, and c is in the rangeof from 0 to 50 in atomic percentages. Alternatively, the amorphousalloy can have the formula (Zr, Ti)_(a)(Ni, Cu)_(b)(Be)_(c), wherein a,b, and c each represents a weight or atomic percentage. In oneembodiment, a is in the range of from 40 to 75, b is in the range offrom 5 to 50, and c is in the range of from 5 to 50 in atomicpercentages. The alloy can also have the formula (Zr, Ti)_(a)(Ni,Cu)_(b)(Be)_(c), wherein a, b, and c each represents a weight or atomicpercentage. In one embodiment, a is in the range of from 45 to 65, b isin the range of from 7.5 to 35, and c is in the range of from 10 to 37.5in atomic percentages. Alternatively, the alloy can have the formula(Zr)_(a)(Nb, Ti)_(b)(Ni, Cu)_(c)(Al)_(d), wherein a, b, c, and d eachrepresents a weight or atomic percentage. In one embodiment, a is in therange of from 45 to 65, b is in the range of from 0 to 10, c is in therange of from 20 to 40 and d is in the range of from 7.5 to 15 in atomicpercentages. One exemplary embodiment of the aforedescribed alloy systemis a Zr—Ti—Ni—Cu—Be based amorphous alloy under the trade nameVitreloy™, such as Vitreloy-1 and Vitreloy-101, as fabricated byLiquidmetal Technologies, CA, USA. Some examples of amorphous alloys ofthe different systems are provided in Table 1 and Table 2.

TABLE 1 Exemplary amorphous alloy compositions Alloy Atm % Atm % Atm %Atm % Atm % Atm % Atm % Atm % 1 Fe Mo Ni Cr P C B 68.00% 5.00% 5.00%2.00% 12.50% 5.00% 2.50% 2 Fe Mo Ni Cr P C B Si 68.00% 5.00% 5.00% 2.00%11.00% 5.00% 2.50% 1.50% 3 Pd Cu Co P 44.48% 32.35%  4.05% 19.11%  4 PdAg Si P 77.50% 6.00% 9.00% 7.50% 5 Pd Ag Si P Ge 79.00% 3.50% 9.50%6.00%  2.00% 5 Pt Cu Ag P B Si 74.70% 1.50% 0.30% 18.0%   4.00% 1.50%

TABLE 2 Additional Exemplary amorphous alloy compositions (atomic %)Alloy Atm % Atm % Atm % Atm % Atm % Atm % 1 Zr Ti Cu Ni Be 41.20% 13.80%12.50%  10.00% 22.50% 2 Zr Ti Cu Ni Be 44.00% 11.00% 10.00%  10.00%25.00% 3 Zr Ti Cu Ni Nb Be 56.25% 11.25% 6.88%  5.63%  7.50% 12.50% 4 ZrTi Cu Ni Al Be 64.75%  5.60% 14.90%  11.15%  2.60%  1.00% 5 Zr Ti Cu NiAl 52.50%  5.00% 17.90%  14.60% 10.00% 6 Zr Nb Cu Ni Al 57.00%  5.00%15.40%  12.60% 10.00% 7 Zr Cu Ni Al 50.75% 36.23% 4.03%  9.00% 8 Zr TiCu Ni Be 46.75%  8.25% 7.50% 10.00% 27.50% 9 Zr Ti Ni Be 21.67% 43.33%7.50% 27.50% 10 Zr Ti Cu Be 35.00% 30.00% 7.50% 27.50% 11 Zr Ti Co Be35.00% 30.00% 6.00% 29.00% 12 Zr Ti Fe Be 35.00% 30.00% 2.00% 33.00% 13Au Ag Pd Cu Si 49.00%  5.50% 2.30% 26.90% 16.30% 14 Au Ag Pd Cu Si50.90%  3.00% 2.30% 27.80% 16.00% 15 Pt Cu Ni P 57.50% 14.70% 5.30%22.50% 16 Zr Ti Nb Cu Be 36.60% 31.40% 7.00%  5.90% 19.10% 17 Zr Ti NbCu Be 38.30% 32.90% 7.30%  6.20% 15.30% 18 Zr Ti Nb Cu Be 39.60% 33.90%7.60%  6.40% 12.50% 19 Cu Ti Zr Ni 47.00% 34.00% 11.00%   8.00% 20 Zr CoAl 55.00% 25.00% 20.00% 

Other exemplary ferrous metal-based alloys include compositions such asthose disclosed in U.S. Patent Application Publication Nos. 2007/0079907and 2008/0118387. These compositions include the Fe(Mn, Co, Ni, Cu) (C,Si, B, P, Al) system, wherein the Fe content is from 60 to 75 atomicpercentage, the total of (Mn, Co, Ni, Cu) is in the range of from 5 to25 atomic percentage, and the total of (C, Si, B, P, Al) is in the rangeof from 8 to 20 atomic percentage, as well as the exemplary compositionFe48Cr15Mo14Y2Cl5B6. They also include the alloy systems described byFe—Cr-Mo-(Y,Ln)-C—B, Co—Cr-Mo-Ln-C—B, Fe—Mn—Cr-Mo-(Y,Ln)-C—B, (Fe, Cr,Co)—(Mo,Mn)—(C,B)—Y, Fe—(Co,Ni)—(Zr,Nb,Ta)—(Mo,W)—B,Fe—(Al,Ga)—(P,C,B,Si,Ge), Fe—(Co, Cr,Mo,Ga,Sb)—P—B—C, (Fe, Co)—B—Si—Nballoys, and Fe—(Cr-Mo)—(C,B)—Tm, where Ln denotes a lanthanide elementand Tm denotes a transition metal element. Furthermore, the amorphousalloy can also be one of the exemplary compositions Fe80P12.5C5B2.5,Fe80P11C5B2.5Si1.5, Fe74.5Mo5.5P12.5C5B2.5, Fe74.5Mo5.5P11C5B2.5Si1.5,Fe70Mo5Ni5P12.5C5B2.5, Fe70Mo5Ni5P11C5B2.5Si1.5,Fe68Mo5Ni5Cr2P12.5C5B2.5, and Fe68Mo5Ni5Cr2P11C5B2.5Si1.5, described inU.S. Patent Application Publication No. 2010/0300148.

The amorphous alloys can also be ferrous alloys, such as (Fe, Ni, Co)based alloys. Examples of such compositions are disclosed in U.S. Pat.Nos. 6,325,868; 5,288,344; 5,368,659; 5,618,359; and 5,735,975, Inoue etal., Appl. Phys. Lett., Volume 71, p 464 (1997), Shen et al., Mater.Trans., JIM, Volume 42, p 2136 (2001), and Japanese Patent ApplicationNo. 200126277 (Pub. No. 2001303218 A). One exemplary composition isFe₇₂Al₅Ga₂P₁₁C₆B₄. Another example is Fe₇₂Al₇Zr₁₀Mo₅W₂B₁₅. Anotheriron-based alloy system that can be used in the coating herein isdisclosed in U.S. Patent Application Publication No. 2010/0084052,wherein the amorphous metal contains, for example, manganese (1 to 3atomic %), yttrium (0.1 to 10 atomic %), and silicon (0.3 to 3.1 atomic%) in the range of composition given in parentheses; and that containsthe following elements in the specified range of composition given inparentheses: chromium (15 to 20 atomic %), molybdenum (2 to 15 atomic%), tungsten (1 to 3 atomic %), boron (5 to 16 atomic %), carbon (3 to16 atomic %), and the balance iron.

The amorphous alloy can also be one of the Pt- or Pd-based alloysdescribed by U.S. Patent Application Publication Nos. 2008/0135136,2009/0162629, and 2010/0230012. Exemplary compositions includePd44.48Cu32.35Co4.05P19.11, Pd77.5Ag6Si9P7.5, andPt74.7Cu1.5Ag0.3P18B4Si1.5.

The aforedescribed amorphous alloy systems can further includeadditional elements, such as additional transition metal elements,including Nb, Cr, V, and Co. The additional elements can be present atless than or equal to about 30 wt %, such as less than or equal to about20 wt %, such as less than or equal to about 10 wt %, such as less thanor equal to about 5 wt %. In one embodiment, the additional, optionalelement is at least one of cobalt, manganese, zirconium, tantalum,niobium, tungsten, yttrium, titanium, vanadium and hafnium to formcarbides and further improve wear and corrosion resistance. Furtheroptional elements may include phosphorous, germanium and arsenic,totaling up to about 2%, and preferably less than 1%, to reduce meltingpoint. Otherwise incidental impurities should be less than about 2% andpreferably 0.5%.

In some embodiments, a composition having an amorphous alloy can includea small amount of impurities. The impurity elements can be intentionallyadded to modify the properties of the composition, such as improving themechanical properties (e.g., hardness, strength, fracture mechanism,etc.) and/or improving the corrosion resistance. Alternatively, theimpurities can be present as inevitable, incidental impurities, such asthose obtained as a byproduct of processing and manufacturing. Theimpurities can be less than or equal to about 10 wt %, such as about 5wt %, such as about 2 wt %, such as about 1 wt %, such as about 0.5 wt%, such as about 0.1 wt %. In some embodiments, these percentages can bevolume percentages instead of weight percentages. In one embodiment, thealloy sample/composition consists essentially of the amorphous alloy(with only a small incidental amount of impurities). In anotherembodiment, the composition includes the amorphous alloy (with noobservable trace of impurities).

In one embodiment, the final parts exceeded the critical castingthickness of the bulk solidifying amorphous alloys.

In embodiments herein, the existence of a supercooled liquid region inwhich the bulk-solidifying amorphous alloy can exist as a high viscousliquid allows for superplastic forming. Large plastic deformations canbe obtained. The ability to undergo large plastic deformation in thesupercooled liquid region is used for the forming and/or cuttingprocess. As oppose to solids, the liquid bulk solidifying alloy deformslocally which drastically lowers the required energy for cutting andforming. The ease of cutting and forming depends on the temperature ofthe alloy, the mold, and the cutting tool. As higher is the temperature,the lower is the viscosity, and consequently easier is the cutting andforming.

Embodiments herein can utilize a thermoplastic-forming process withamorphous alloys carried out between Tg and Tx, for example. Herein, Txand Tg are determined from standard DSC measurements at typical heatingrates (e.g. 20° C./min) as the onset of crystallization temperature andthe onset of glass transition temperature.

The amorphous alloy components can have the critical casting thicknessand the final part can have thickness that is thicker than the criticalcasting thickness. Moreover, the time and temperature of the heating andshaping operation is selected such that the elastic strain limit of theamorphous alloy could be substantially preserved to be not less than1.0%, and preferably not being less than 1.5%. In the context of theembodiments herein, temperatures around glass transition means theforming temperatures can be below glass transition, at or around glasstransition, and above glass transition temperature, but preferably attemperatures below the crystallization temperature T_(x). The coolingstep is carried out at rates similar to the heating rates at the heatingstep, and preferably at rates greater than the heating rates at theheating step. The cooling step is also achieved preferably while theforming and shaping loads are still maintained.

Electronic Devices

The embodiments herein can be valuable in the fabrication of electronicdevices using a BMG. An electronic device herein can refer to anyelectronic device known in the art. For example, it can be a telephone,such as a cell phone, and a land-line phone, or any communicationdevice, such as a smart phone, including, for example an iPhone™, and anelectronic email sending/receiving device. It can be a part of adisplay, such as a digital display, a TV monitor, an electronic-bookreader, a portable web-browser (e.g., iPad™), and a computer monitor. Itcan also be an entertainment device, including a portable DVD player,conventional DVD player, Blue-Ray disk player, video game console, musicplayer, such as a portable music player (e.g., iPod™), etc. It can alsobe a part of a device that provides control, such as controlling thestreaming of images, videos, sounds (e.g., Apple TV™), or it can be aremote control for an electronic device. It can be a part of a computeror its accessories, such as the hard drive tower housing or casing,laptop housing, laptop keyboard, laptop track pad, desktop keyboard,mouse, and speaker. The article can also be applied to a device such asa watch or a clock.

Embodiments

An embodiment provided herein includes a method of forming an article byproviding a foam material, and insert casting onto the foam material abulk-solidifying amorphous alloy to form the article. The foam materialcan be used as an integral part of the article to improve or otherwisealter the properties of the bulk-solidifying amorphous alloy that isinsert cast into or on the foam. In addition, the foam material can beused as a processing aid to enable the formation of bulk-solidifyingamorphous alloy materials that otherwise could not have been formedusing conventional processing techniques (e g, making an article havinga thickness greater than the critical casting thickness of thebulk-solidifying amorphous alloy alone).

Another embodiment provides a method of making an article that includesproviding a foam material, insert casting onto the foam material abulk-solidifying amorphous alloy, removing the foam, and optionallyinserting another metal or bulk-solidifying amorphous alloy to replacethe removed foam. The foam material can be removed from the article byetching, melting, etc., thereby leaving a bulk-solidifying amorphousarticle with voids where the foam previously existed. These voids canremain in the article, or may be filled with a different material, orfilled with the same bulk-solidifying amorphous alloy to provide thefinal article.

Another embodiment provides an article comprised of a bulk-solidifyingamorphous alloy and a foam. In one embodiment, the article includes of alaminate of bulk-solidifying amorphous alloy and a foam. In anotherembodiment, the article includes a bulk-solidifying amorphous alloyhaving a thickness greater than the critical casting thickness,optionally including a foam, or having dispersed therein a metal or abulk-solidifying amorphous alloy

Any foam material can be used in the embodiments so long as it iscapable of withstanding the insert casting processing conditions bywhich the bulk-solidifying amorphous metal is cast into and on the opencell metal foam. Suitable foam materials include hard polymeric foams,metal foams, ductile metal foams, ceramic foams, and the like. In oneembodiment, the foam is an open cell metal foam, which is intended todenote a metal foam having intersticies or voids that extend throughoutthe material, and provide at least one channel from one surface of thefoam to the opposing surface.

An exemplary open cell metal foam is shown in FIG. 3, a scanningelectron micrograph of a metal foam, magnified 10 times. As shown, themetal foam 300 includes a metal lattice structure 310 that includes aplurality of voids 320 that extend throughout the foam material. Thesevoids 320 can be filled with a bulk-solidifying amorphous alloy materialand the surface coated with the bulk-solidifying amorphous alloymaterial to provide a final article that has dimensions greater than thecritical casting dimensions of the bulk-solidifying amorphous alloymaterial. In addition, the specific metal and porosity of the metal foamcan be selected to provide certain properties (e.g., ductility, thermaland/or electrical conductivity, etc.) to the final article that are nototherwise available using bulk-solidifying amorphous alloy materials.For example, it is known that bulk-solidifying amorphous alloy materialscan be brittle due to their hardness, but use of a more ductile opencell metal foam may provide a final article that still benefits from thehardness of the bulk-solidifying amorphous alloy, but is not as brittleas the bulk-solidifying amorphous alloy material itself. The presence ofthe metal foam therefore may create a composite material with thebulk-solidifying amorphous alloy material.

Suitable metal foams may be made by any conventional techniques known inthe art. The embodiments may make use of the metal foams disclosed in,for example, U.S. Pat. Nos. 5,588,477, 5,679,041, 5,738, 907, 5,951,791,6,678,182, and 7,328,831, the disclosures of which are incorporated byreference herein in their entireties. In one embodiment, the metal foamsubstrate is not removed, but rather remains during bulk-solidifyingamorphous alloy filling and becomes an integral part of the finishedproduct. More specifically, a metal foam substrate is used whichcomprises a plurality of randomly oriented ligaments 310 interconnectedby a plurality of nodes 330 that together form a three-dimensionalreticulum defining a multitude of interstitial voids 320 the comprisecells. The metal foam substrate may comprise the same, essentially thesame (i.e., alloys of), or an entirely different metal than thebulk-solidifying amorphous alloy material, depending on the needs of thefinal product being produced. Hence, for example, the open cell metalfoam may comprise aluminum, magnesium, nickel, iron, copper, etc.

One metal foam, useful in the embodiments, may be formed byelectrodepositing a layer of metal onto a fugitive foam substrate (i.e.,polyurethane) such as described in U.S. Pat. No. 3,694,325, thedisclosure of which is incorporated by reference herein in its entirety.The fugitive foam is then burned-off leaving a hollow metal network.Another metal foam useful with the embodiments may be formed bydepositing metal particles onto a fugitive substrate, and then sinteringthe particles together while concurrently removing the substrate. Stillother foams made by directional solidification may be used. One suchdirectionally solidified aluminum foam, for example, is sold under thetrade name DUOCEL® by the ERG Materials and Aerospace Corporation hasbeen used effectively.

In accordance with an embodiment, the open-cell, metallic foam may beimpregnated with a slurry of filler particles suspended in a fugitivevehicle, in which the filler particles serve to modify the mechanicalproperties of the metal foam and resulting final article. The vehicleused to carry the particles into the metal foam substrate may compriseany of a variety of fluids including organics such as wax, polystyrene,polyethylene, methyl cellulose/H₂O gel, etc., or simply water, forfilling the polymeric foam. While an aqueous sedimentation process maybe used with metal foam, preferably the particles will be thoroughlymixed with an organic binder and injected under pressure into a moldcontaining the substrate. One such binder comprises eighty (80) weightpercent diphenyl carbonate and twenty (20) weight percent polystyrene.After pre-blending at 120° C., the binder is mixed with the desiredfiber or particulate volume fraction by using a roller blade mixer, asigma blade mixer or twin-screw extruder. The feedstock then can beextruded and pelletized for introduction into an injection moldingmachine. The metallic foam can be inserted into a die of the same orother shape, and the feedstock melted by the action of the molding screwand injected into the die under pressure, infiltrating theinterconnected pores of the foam from the gate to the end-of-fill. Thefoam aids in the reduction of shrink-related voids by serving asalready-dense filler. The use of injection molding to infiltratereinforcement is not limited to metal networks, but may also be usedwith relatively rigid polymer foams as well.

If a filler were optionally used as described above, followingimpregnation of the metal foam substrate with the slurry, the vehiclewould be removed so as to leave the filler particles entrained withinthe interstitial cells/pores of the metal foam substrate. In the case oforganic/polymeric vehicles, removal is preferably effected by heatingthe particle-filled foam sufficiently to volatize or burn-off thevehicle. With the metal foam substrate present, this burn-off can beachieved more quickly than if there were no such substrate present andwithout fear of distorting the foam material. Alternatively, the organicvehicle may be removed by dissolution in an appropriate solvent, or byetching. A combination of solvent and heat removal has been demonstratedfor vehicles comprising a mixture of two or more organic ingredients. Ifa polymeric binder were used, e.g., diphenyl carbonate, this binder maybe removed by dissolution in warm methanol and the remaining polymerremoved by thermal treatment to 600° C. For aluminum foams, which arelow-melting and easily-oxidized, the heat-treatment can be done in anon-oxidizing atmosphere (Ar, N₂) to 450° C. Aqueous vehicles are mostsimply removed by heating to drive off the water and dry theparticle-filled metal foam. Metal foam substrates having cell/pore sizesbetween about 500 microns and 2000 microns permit particle loadings upto about 15% by volume to about 70% by volume respectively with amaximum of about 45% by volume when the particles are fibrils havingaspect ratios greater than about 10.

In certain embodiments, the metal in the foam tends to melt, at least onits surface, and weld with the bulk-solidifying amorphous alloy beinginsert cast into and onto the foam. In other embodiments, somealloying/diffusion bonding may occur at the interfaces between the metalfoam and the bulk-solidifying amorphous alloy. Preheating of the metalfoam to about 200° to 800° C. may facilitate impregnation of thebulk-solidifying amorphous alloy material.

Insert casting may be carried out to form the final article. In oneembodiment, insert casting may be carried out by pouring molten orsemi-molten bulk-solidifying amorphous alloy into the at least onecavity 320, and then cooling the product to form a metal-to-metal bondbetween the metal foam and the bulk-solidifying amorphous alloymaterial. The metal-to-metal bond also may be formed byalloying/diffusion bonding, and/or by melting a portion of the metalfoam material 300 which in turn welds with the bulk-solidifyingamorphous alloy material. Alternatively, the at least one surface of thecavity 320 may be treated with a material that facilitates ametal-to-metal bond, such as a thin foil that will deform, melt, orotherwise fuse to the bulk-solidifying amorphous alloy during the insertcasting procedure. In another embodiment, the at metal foam material 300may be treated to facilitate the metal-to-metal bond, for example, by ablasting treatment with a nonmetallic abrasive, or using a surfaceroughening treatment such as contact with an acid.

In another embodiment, after the metal foam material 300 has been filledwith bulk-solidifying amorphous alloy material, another thin sheet ofbulk-solidifying amorphous alloy could be deposited in one or moresurfaces of the filled metal foam. The laminate structure then can beheated and thermally plastically formed so that the final articleprovides a smooth surface of bulk-solidifying amorphous alloy with ametal foam material positioned underneath. The metal foam in thisembodiment could be etched away and replaced with another material,including the same bulk-solidifying amorphous alloy or anotherbulk-solidifying amorphous alloy material having different properties.Alternatively, the metal foam could be etched away leaving a porousbulk-solidifying amorphous alloy material that is then laminated withone or more thin sheets of bulk-solidifying amorphous alloy.

One exemplary method of insert casting a bulk-solidifying amorphousalloy material into and onto a foam material is shown in FIG. 4. Themethod is particularly suitable for use in fabricating articles having athickness greater than the critical casting thickness of thebulk-solidifying amorphous alloy material. For example, if the criticalcasting thickness of a particular bulk-solidifying amorphous alloymaterial is 3 mm, but the final product must be 6 mm or more, simplyfabricating a bulk-solidifying amorphous alloy material might not bepossible given this required thickness. In this embodiment, a foammaterial 300, for example a metal open cell foam material may beprovided, having a thickness t. Thickness t may be on the order of 3-5mm, for example. The bulk-solidifying amorphous alloy material can beinsert cast into and on the surface of the foam material 300 to providean article with a larger thickness T, for example, 6-8 mm in thickness.The bulk solidifying amorphous alloy material may form a skin 410 aroundthe foam 300, and may infiltrate the foam to fill some or all of thevoids to provide a filled foam 420.

It is preferred in the embodiments that the foam material 300 becompatible with the insert casting processes so that it can form anintegral structure with the bulk-solidifying amorphous alloy material.The foam 300 should be capable of absorbing some of the heat of thebulk-solidifying amorphous alloy material as it is cast into and on thefoam 300. Typical casting temperatures may be on the order of 900° C.,whereas the temperature of the foam may only be on the order of 200° C.In some embodiments, the foam may be connected to a heat source topre-heat the foam, or may be connected to a heat sink the withdrawsheat. For example, there may be embodiments in which the entire centerof the article is intended to be either completely hollow, or filledwith another material (e.g., a material having high thermalconductivity, such as copper). In this embodiment, it may be useful tocool the center portion of the foam so that no bulk-solidifyingamorphous alloy infiltrates that far into the foam. Thus, the metal foamwill exist by itself in the center and can be melted or etched away toleave a hollow portion. Those skilled in the art will appreciate thatthe foam may be selectively heated and cooled to provide the desiredinternal geometry of the final article.

In other embodiments, the foam 300 may be designed to have certainfeatures the extend from the surface of the final article, such asexternal pins or threads. The bulk-solidifying amorphous alloy then canform a thin skin on the surface of the foam 300, leaving the externalpins or threads un-coated. In other embodiments, the foam may be aceramic foam or other foam material capable of withstanding the insertcasting conditions, in which portions of the foam are intended to beflush with the surface of the bulk-solidifying amorphous alloy. Thiscould be accomplished by using a foam having a tooth-like structurewhere the bulk-solidifying amorphous alloy fills in the foam and forms askin on the surface in the areas that do not include the protrudingteeth. This embodiment might be particularly useful in designing anantenna for use in an electronic device. In yet another embodiment, theinsert casting process may result in a material that does not form anexternal skin on the surface of the foam 300. This material may beuseful as a composite material, or could be laminated with one or moresheets of bulk-solidifying amorphous alloy to form a laminate structuresimilar to that shown on the top right of FIG. 4.

An optional embodiment is shown in FIG. 4 where the insert castfoam/bulk-solidifying amorphous alloy material is further processed toremove the foam structure. This can be accomplished by etching away thematerial that makes up the ligaments 310 and nodes 330 (FIG. 3) or bymelting the material and removing it from the article. If thebulk-solidifying amorphous alloy material filled most of the voids 320in the foam 300, this optional process will result in a matrix ofbulk-solidifying alloy 430 within or underneath a bulk-solidifyingamorphous alloy skin 410. As stated above, controlling the coolingcharacteristics of the foam during insert casting can affect the degreeto which the bulk-solidifying amorphous alloy material infiltrates thevoids 320 in the foam 300. In addition, the size of the voids 320 alsocan modify the degree to which the bulk-solidifying amorphous alloymaterial infiltrates the voids 320 in the foam 300. If thebulk-solidifying amorphous alloy material does not infiltrate the voids320 all the way to the center of the foam material 300, then thisoptional removal process will result in a substantially hollow center.The material then may be used as is, or further processed as describedbelow.

Another optional process is to fill the voids left after the removalprocess, either partially or fully. Any material can be used to fill thevoids in the matrix 430, depending on the final product characteristics.For example, if the final product is to have improved conductivity, thevoids in matrix 430 may be filled with a conductive material such ascopper to provide a filled, or partially filled matrix 440. Othermaterials can be used to improve the thermal conductivity, orresistivity of the product. Alternatively, the voids in matrix material430 may be filled with the same or different bulk-solidifying amorphousalloy to provide a final product having a thickness greater than thecritical casting thickness of the bulk-solidifying amorphous alloy.

The methods described herein are useful in providing final articleshaving a variety of desired shapes and physical characteristics. Forexample, a metal band surrounding a hand-held electronic device can befabricated from a bulk-solidifying amorphous alloy material to provide ahard metal band, but various types of foam materials can be used invarious portions of the band to provide desirable characteristics to theband. For example, in areas where increased strength is desired, (e.g.,in the corners or other areas typically encountering wear and tear), afoam having smaller voids 320 and thicker ligaments 310, or struts, canbe used. In areas where a more ductile material is need, for examplesurrounding input ports, or metal pin ports, a more ductile foam couldbe used. These foam materials may be placed in the appropriate positionsin the mold, a bulk-solidifying amorphous alloy material then insertcast into the mold to produce the final desired shape of the band, andthen select areas of the band could be further processed by etching andthen optionally filling to provide greater thermal conductivity orelectrical conductivity in certain areas.

An illustrative portable electronic device in accordance with anembodiment of the present invention is shown in FIG. 5. Device 10 ofFIG. 5 may be, for example, a handheld electronic device that supports2G, 3G, and/or 4G cellular telephone and data functions, globalpositioning system capabilities, and local wireless communicationscapabilities (e.g., IEEE 802.11 and Bluetooth®) and that supportshandheld computing device functions such as internet browsing, email andcalendar functions, games, music player functionality, etc. Device 10may have housing 12, or band. Antennas for handling wirelesscommunications may be housed within housing 12 (as an example), and canbe provided by the process described above.

Housing 12, which is sometimes referred to as a case or band, can befabricated from a composite bulk-solidifying amorphous alloy/foammaterial made in accordance with the embodiments described herein. In apreferred embodiment, one or more portions of the housing may beprocessed to form a part of the antennas in device 10. For example,metal portions of housing 12 may be shorted to an internal ground planein device 10 to create a larger ground plane element for that device 10.

Housing 12 may have a bezel 14. The bezel 14 may be formed from aconductive material or other suitable material. Bezel 14 may serve tohold a display or other device with a planar surface in place on device10 and/or may serve to form an esthetically pleasing trim around theedge of device 10. As shown in FIG. 5, for example, bezel 14 may be usedto surround the top of display 16. Bezel 14 and/or other metal elementsassociated with device 10 may be used as part of the antennas in device10. For example, bezel 14 may be shorted to printed circuit boardconductors or other internal ground plane structures in device 10 tocreate a larger ground plane element for device 10.

Display 16 may be a liquid crystal display (LCD), an organic lightemitting diode (OLED) display, or any other suitable display. Theoutermost surface of display 16 may be formed from one or more plasticor glass layers. If desired, touch screen functionality may beintegrated into display 16 or may be provided using a separate touch paddevice. An advantage of integrating a touch screen into display 16 tomake display 16 touch sensitive is that this type of arrangement cansave space and reduce visual clutter.

Display screen 16 (e.g., a touch screen) is merely one example of aninput-output device that may be used with electronic device 10. Ifdesired, electronic device 10 may have other input-output devices. Forexample, electronic device 10 may have user input control devices suchas button 19, and input-output components such as port 20 and one ormore input-output jacks (e.g., for audio and/or video). Button 19 maybe, for example, a menu button. Port 20 may contain a 30-pin dataconnector (as an example). Openings 22 and 24 may, if desired, formspeaker and microphone ports. Speaker port 22 may be used when operatingdevice 10 in speakerphone mode. Opening 23 may also form a speaker port.For example, speaker port 23 may serve as a telephone receiver that isplaced adjacent to a user's ear during operation. In the example of FIG.5, display screen 16 is shown as being mounted on the front face ofhandheld electronic device 10, but display screen 16 may, if desired, bemounted on the rear face of handheld electronic device 10, on a side ofdevice 10, on a flip-up portion of device 10 that is attached to a mainbody portion of device 10 by a hinge (for example), or using any othersuitable mounting arrangement.

A user of electronic device 10 may supply input commands using userinput interface devices such as button 19 and touch screen 16. Suitableuser input interface devices for electronic device 10 include buttons(e.g., alphanumeric keys, power on-off, power-on, power-off, and otherspecialized buttons, etc.), a touch pad, pointing stick, or other cursorcontrol device, a microphone for supplying voice commands, or any othersuitable interface for controlling device 10. Although shownschematically as being formed on the top face of electronic device 10 inthe example of FIG. 5, buttons such as button 19 and other user inputinterface devices may generally be formed on any suitable portion ofelectronic device 10. For example, a button such as button 19 or otheruser interface control may be formed on the side of electronic device10. Buttons and other user interface controls can also be located on thetop face, rear face, or other portion of device 10. If desired, device10 can be controlled remotely (e.g., using an infrared remote control, aradio-frequency remote control such as a Bluetooth® remote control,etc.).

Electronic device 10 may have ports such as port 20. Port 20, which maysometimes be referred to as a dock connector, 30-pin data portconnector, input-output port, or bus connector, may be used as aninput-output port (e.g., when connecting device 10 to a mating dockconnected to a computer or other electronic device). Port 20 may containpins for receiving data and power signals. Device 10 may also have audioand video jacks that allow device 10 to interface with externalcomponents. Typical ports include power jacks to recharge a batterywithin device 10 or to operate device 10 from a direct current (DC)power supply, data ports to exchange data with external components suchas a personal computer or peripheral, audio-visual jacks to driveheadphones, a monitor, or other external audio-video equipment, asubscriber identity module (SIM) card port to authorize cellulartelephone service, a memory card slot, etc. The functions of some or allof these devices and the internal circuitry of electronic device 10 canbe controlled using input interface devices such as touch screen display16.

Components such as display 16 and other user input interface devices maycover most of the available surface area on the front face of device 10(as shown in the example of FIG. 5) or may occupy only a small portionof the front face of device 10. Because electronic components such asdisplay 16 often contain large amounts of metal (e.g., asradio-frequency shielding), the location of these components relative tothe antenna elements in device 10 should generally be taken intoconsideration. Suitably chosen locations for the antenna elements andelectronic components of the device will allow the antennas ofelectronic device 10 to function properly without being disrupted by theelectronic components.

Examples of locations in which antenna structures may be located indevice 10 include region 18 and region 21. These are merely illustrativeexamples. Any suitable portion of device 10 may be used to house antennastructures for device 10 if desired. In this embodiment, thebulk-solidifying amorphous alloy/foam composite material may be furtherprocessed in these areas by etching and then filling partially or whollythe voids (or hollow portions) remaining after etching with metalssuitable for use in an antennae.

The area of housing or band 12 surrounding ports 20, 22, and 24, forexample, may be designed to have a greater ductility or flexibility thanother areas of housing 12. Use of a brittle bulk-solidifying amorphousalloy material in these areas may result in some of the material beingbroken, as connector pins, antenna jacks and other input devices arerepeatedly inserted and withdrawn from the respective ports 20, 22, and24. In these areas, a more ductile metal foam may be used having alarger pore size, for example, than foam used in other portions of thehousing 12.

The pore size and strut size of the foam 300 also can be modified toprovide structural support to the housing 12, for example, in and aroundthe corners. The pore size also can be modified in certain areas to bevery small to avoid catastrophic failure in the event pot cracks form onthe surface of housing 12. Use of a bulk-solidifying amorphousalloy/foam composite material in which the foam has small pore sizes canhelp reduce the formation of severe cracks and breaks in the surface ofhousing 12, in the event a pot crack forms on the surface thereof.

The methods of the embodiments described herein are useful in providingbulk-solidifying amorphous alloy/foam composite materials havingspecifically tailored characteristics. Bulk-solidifying amorphousalloy/foam composite materials can be designed to have superior strengthin one portion by use of a foam having thicker struts, and at the sametime have improved flexibility and less brittleness in other portions byuse of a more ductile foam. Other areas of the bulk-solidifyingamorphous alloy/foam composite materials may be hollow or treated toremove the foam and then subsequently filled with more bulk-solidifyingamorphous alloy, with a thermally conductive material, with anelectronically conductive material, and the like. Those skilled in theart will appreciate that insert casting a bulk-solidifying amorphousalloy into a foam material, preferably a metal open cell foam, canprovide a final bulk-solidifying amorphous alloy/foam composite materialhaving many different properties, most if not all of which could not beachieved through use of the bulk-solidifying amorphous alloy materialalone.

One of the embodiments described herein provides for an optional etchingprocess in which the material used to make the foam is etched away afterinsert casting with a bulk-solidifying amorphous alloy. Suitableetchable materials that may be used to fabricate the foam include thosethat are “wet” etchable and those that are “dry” etchable. Dry-etchablematerials are those that can be etched with a particular gas, such as achlorine based gas, or a fluorine based gas. Suitable materials for dryetching include, for example, chromium, chromium nitride, chromiumoxide, chromium oxynitride, and chromium oxycarbonitride, tantalumnitride, tantalum oxide, and mixtures thereof. Other suitable etchablematerials that may be wet-etched include, for example, metal oxides andnitrides of Zr, Hf, La, Si, Y, Indium, and Al, photoresist resins,brass, gold, copper, beryllium-copper, molybdenum, nickel, nickelsilver, phosphorous-Bronze, platinum, silicon, Carbon Steel, stainlesssteel, spring steel, titanium, titanium nitride, tungsten, zinc, Monel,and alloys and mixtures thereof. Any suitable etching material may beused, depending on whether the etchable material 330 is a dry-etchablematerial or a wet-etchable material. Suitable wet-etching materialsinclude acids such as hydrofluoric acid, sulfuric acid, or otheretchants such as sodium hydroxide, ethylene diamine pyrocatechol (EDP),potassium hydroxid/isopropyle alcohol (KOH/IPA), tetramethylammoniumhydroxide (TMAH), and the like. Dry-etchants and dry-etching processes,or those used in plasma etching, may include gases containing chlorineor fluorine, such as, for example, carbon tetrachloride, oxygen (foretching ash photoresist), ion milling or sputter etching using noblegases such as argon, reactive-ion etching, and deep reactive-ionetching. The following table provides suitable etchants (wet and dry)that can be used to etch various etchable materials.

Etchants for Specified material Plasma Material to be etched Wetetchants etchants Aluminium (Al) 80% phosphoric acid (H₃PO₄) + 5% aceticacid + Cl₂, CCl₄, 5% nitric acid (HNO₃) + 10% water (H₂O) at 35-45° C.;or SiCl₄, BCl₃ sodium hydroxide Indium tin oxide [ITO] Hydrochloric acid(HCl) + nitric acid (HNO₃) + water (H₂O) (In₂O₃:SnO₂) (1:0.1:1) at 40°C. Chromium (Cr) Chrome etch: ceric ammonium nitrate ((NH₄)₂Ce(NO₃)₆) +nitric acid (HNO₃) Hydrochloric acid (HCl) Copper Cupric oxide, ferricchloride, ammonium persulfate, ammonia, 25-50% nitric acid, hydrochloricacid, and hydrogen peroxide Gold (Au) Aqua regia Molybdenum (Mo) CF₄Organic residues and Piranha etch: sulfuric acid (H₂SO₄) + hydrogenperoxide (H₂O₂) O₂ (ashing) photoresist Platinum (Pt) Aqua regia Silicon(Si) Nitric acid (HNO₃) + hydrofluoric acid (HF) CF₄, SF₆, NF₃ Cl₂,CCl₂F₂ Silicon dioxide (SiO₂) Hydrofluoric acid (HF) CF₄, SF₆, NF₃Buffered oxide etch [BOE]: ammonium fluoride (NH₄F) and hydrofluoricacid (HF) Silicon nitride (Si₃N₄) 85% Phosphoric acid (H₃PO₄) at 180° C.(Requires SiO₂ etch CF₄, SF₆, NF₃ mask) Tantalum (Ta) CF₄ Titanium (Ti)Hydrofluoric acid (HF) BCl₃ Titanium nitride (TiN) Nitric acid (HNO₃) +hydrofluoric acid (HF) SCl Buffered HF (bHF) Tungsten (W) Nitric acid(HNO₃) + hydrofluoric acid (HF) CF₄ Hydrogen Peroxide (H₂O₂) SF₆

Etchable materials 330 and the etchants that can be used to selectivelyremove them are described, for example, in Wolf, S.; R. N. Tauber(1986), Silicon Processing for the VLSI Era: Volume 1-ProcessTechnology. Lattice Press. pp. 531-534, 546; Walker, Perrin; William H.Tarn (1991), CRC Handbook of Metal Etchants. pp. 287-291; and Kohler,Michael (1999). Etching in Microsystem Technology. John Wiley & Son Ltd.p. 329. Those having ordinary skill in the art will be capable ofutilizing a suitable etchable material to fabricate the foam 300depending on the desired thickness, the geometry, and the make-up of thefinal article, using the guidelines provided herein.

While the invention has been described in detail with reference toparticularly preferred embodiments, those skilled in the art willappreciate that various modifications may be made thereto withoutsignificantly departing from the spirit and scope of the invention.

1-17. (canceled)
 18. An article comprised of a bulk-solidifyingamorphous alloy and a metal foam.
 19. The article of claim 18, whereinthe article comprises a laminate of bulk-solidifying amorphous alloy anda metal open cell foam.
 20. The article of claim 18, wherein the articlehas a thickness greater than the critical casting thickness of thebulk-solidifying amorphous alloy.
 21. The article of claim 18, whereinthe article comprises an electronic device.
 22. The article of claim 21,wherein the electronic device selected from the group consisting of atelephone, a cell phone, a land-line phone, a smart phone, an electronicemail sending/receiving device a television, an electronic-book reader,a portable web-browser, a computer monitor, a DVD player, a Blue-Raydisk player, a video game console, a music player, a device thatprovides controlling the streaming of images, videos, and sounds, aremote control, a watch, and a clock.